Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $63.48   12.489%   $71.408   $71.41   $71.40   $71.40  
  Purchase #2 $182.62   12.726%   $205.8602   $205.86   $205.85   $205.90  
  Purchase #3 $80.81   13.867%   $92.0159   $92.02   $92.00   $92.00  
  Purchase #4 $208.51   10.634%   $230.683   $230.68   $230.70   $230.70  
  Purchase #5 $181.59   13.535%   $206.1682   $206.17   $206.15   $206.20  
  Purchase #6 $243.38   4.710%   $254.8432   $254.84   $254.85   $254.80  
  Purchase #7 $247.29   7.414%   $265.6241   $265.62   $265.60   $265.60  
  7 purchase totals = $1,207.68       $1,326.6026   $1,326.60   $1,326.55   $1,326.60